I had the exact same problem as yours. ***None*** of the solutions offered online for opening the Soundsticks II speaker housing worked for me. What finally worked was to carefully grab the perforated cover of the affected speaker with hemostats (using 2 pairs at once, top and bottom) and ''pull, not push'', the speaker back into place.
I tried doing this by pulling wire through the perforations, but didn't have wire that is both strong (like a paper clip) and flexible (like a twist tie) enough for the job. Maybe the right paper clip would do it.
One half of the speaker can go in fairly easily, but pulling both sides in can be difficult. I added super glue to one side, pulled that side in, waited briefly, then pulled the other side of the speaker in.
When doing this it’s important to make sure alignment is correct. Each speaker fits only one way, with no angular deviation.
I worried that the perforated cover would break, but it didn't. It scratched some through the ordeal, though.